An example of a borehole for which the present invention would be useful is a borehole drilled to produce hydrocarbons from a hydrocarbon-containing formation. To prevent collapse of the wall of the borehole, the borehole is cased by means of a casing arranged in the borehole. The casing is fixed in the borehole by a cement layer between the outer wall of the casing and the inner wall of the borehole.
The borehole is not cased where it traverses the hydrocarbon-containing formation to allow substantially unrestricted influx of fluids from the hydrocarbon-containing formation into the borehole. When the hydrocarbon-containing formation is so weak that it will collapse, the uncased borehole section is completed with a liner. The liner is provided with slots to allow fluid influx into the borehole.
A known method of completing an uncased section of a borehole in an underground formation comprises the steps of placing a slotted liner in the borehole at the location of the hydrocarbon-containing formation and fixing the liner. Fixing the liner is usually accomplished by securing the upper end of the liner to the lower end of the casing arranged in the borehole.
Because the inner diameter of the cased section is less than the diameter of the borehole, and the slotted liner has to be lowered through the cased section of the borehole, the diameter of the slotted liner is smaller than the diameter of the borehole. Thus there is an annular space between the liner and the wall of the borehole. With time the formation will collapse and settle against the outer wall of the liner so that the annular space gets filled with particulates. When hydrocarbons are produced, the fluid will flow through the formation, through the filled annular space and through the slots in the liner into the cased borehole. The circumference through which fluids flow into the cased borehole is thus reduced from the circumference of the borehole to the circumference of the outer wall of the liner.
Reference is made to U.S. patent specification No. 1,135,809 disclosing completing an uncased section of a borehole with a slotted liner having overlapping slots. This publication, however, does not disclose expanding the slotted liner.
It is therefore an object of the present invention to provide a method of completing an uncased section of a borehole, wherein optimal use is made of the circumference of the borehole to reduce resistance to fluid flow as much as possible.